Herbs which are members of the Labiatae family have been used for culinary purposes since time immemorial. This botanical group, commonly known as the mint family, includes not only peppermint and spearmint, but also sage, thyme, rosemary, marjoram, catnip, and others. These herbs have been used for both their flavoring and preserving qualities, sage and rosemary in particular being widely used in pork sausage and poultry seasonings to retard rancidity. In herbal dressings and sauces, marjoram, thyme, and the mints are used for the same purpose.
Until modern technology was able to make herbal extracts which retained both the flavor and antioxidant-preservative qualities of the parent herb from which they were derived, the extracts played a very small role in seasonings in the food industry. Now, however, it is possible to make herbal extracts which are stable, uniform in flavor, sterile, and without extraneous matter such as sticks and sand, and which retain the desired flavoring components of the dried herb. As a result, these extracts are becoming more and more widely used in the food processing industry.
These extracts are commonly known as oleoresins. They are made by percolating the herb with an approved food-grade solvent such as a lower alcohol (methanol, ethanol, isopropanol), a lower-alkyl ketone (acetone, methyl ethyl ketone), petroleum ether (hexane, etc.), and less preferably with a chlorinated solvent such as methylene chloride or ethylene dichloride. Extraction temperatures range from ambient up to the boiling point of the solvent, and generally the herb is exhaustively extracted insofar as the given solvent is concerned. A solvent such as ethanol will tend to extract more glycolipids and sugars than a ketone or chlorinated solvent, which in turn are more powerful solvents and less selective than hexane.
Although the crude oleoresin is suitable for many purposes, it is often refined to remove chlorophyll by charcoal adsorption and perhaps washed with water to remove sugars It may often be subjected to vacuum distillation to remove undesirable aromas present in the natural herb, such as dimethyl sulfide and terpene hydrocarbons. In the case of rosemary, Chang (U.S. Pat. No. 3,950,266) describes a distillation process which will remove camphor, which is often an undesirable component, and the desirable rosemary aromas remain in the refined oleoresin if the procedure is terminated at the proper time.
Because rosemary is the member of the mint family on which the most effort on refining has been expended, the prior art is best exemplified by discussing the kinds of products which have been made from it, and the procedures by which they have been obtained The same types of products and procedures apply equally well to other Labiatae.
Crude oleoresin rosemary, made by using the FDA-approved solvents already described, is available in many forms, such as the semisolid, resinous straight extract, an extract homogenized with an edible carrier such as vegetable oil or emulsifier, or in the form of an oil and water-dispersible blend as described in Todd (U.S. Pat. Nos. 4,283,429; 4,285,981; 4,315,947; and 4,343,823). All of these forms induce a haze or precipitate when added to a vegetable oil at the level of use (usually about 1 to 5,000), and they will throw precipitates which do not redissolve upon standing. By the method of Chang they may, however, be standardized as to the desired flavoring effect and undesirable odoriferous materials removed. They are not water soluble.
The antioxidant power of rosemary has been known and studied for many years. Specific compounds have been identified which have antioxidant properties, and among these are carnesol, carnosic acid, rosmaridiphenol, and rosmanol.
The latter compound was patented by Nakatani (U.S. Pat. No. 4,450,097). Weight for weight, these compounds are about as effective as the present synthetic antioxidants used in food. However, the known and described substances are only a small fraction of the total antioxidant materials present in rosemary and, from an economic point of view, their separation from the other active substances in the extract does not make sense.
A method of extracting rosemary not dependent upon an organic solvent, but rather using water at a pH of preferably about 8.6, is described in Viani (U.S. Pat. No. 4,012,531). Using water as a solvent avoids the expense of an organic solvent, but it also extracts glycolipiids and sugars, etc., and his extract therefore contains substances unwanted in many applications. He limits his pH to below 10.5. At the preferred pH described in his examples, only about 60 to 70% of the antioxidant materials are recovered.
Viani uses about ten parts of) water to one part of rosemary for his extraction, so his solution is very dilute (the antioxidant is present at 1% or less in the water). The murky water dispersion may be used immediately, but within a few days it loses its antioxidant power. An obvious explanation is that the polyphenolic substances with structures like rosmanol, carnesol, carnosic acid, etc., are unstable in such dilute alkaline solutions. Perhaps to overcome this lack of stability, Viani suggests precipitation of the antioxidant materials by prompt acidification of the alkaline extract, and separation of the precipitate. This acidified precipitate is stable, but dissolves in fats only partially even upon intense heating and stirring with precipitation developing on cooling, and is not soluble or dispersible in water, but may be partially redispersed on the addition of base. A third alternative is to evaporate the water, leaving an alkaline solid which shares the instability of his alkaline water solution. It is not soluble in fats at any temperature, and cannot be redissolved in water to form a clear precipitate-free solution.
Paton (U.S. Pat. No. 3,497,362) describes making either a powdered crude extract of rosemary, or an ethanolic solution of a crude extract, and dispersing either the acidic powder or the dilute ethanolic solution of the acidic powder in phosphate solution, which in turn is used to improve the quality of vegetables upon drying. His powder, similar to the acidified powder of Viani, provides a means for storing the active antioxidants in stable form. The uniquely stable alkaline product of this invention permits admixing with phosphate to give a solution rather than a dispersion, and without extraneous insoluble substances, and without losing stability even though it is in liquid form.
Nakatani (U.S. Pat. No. 4,450,097, previously cited) combines the solvent extraction technique of preparation of the oleoresin with Viani's technique of aqueous extraction, to prepare both a highly concentrated fraction of the antioxidants, as well as to prepare rosmanol. In his examples, he extracts rosemary with hexane at ambient temperature, which removes about 60% to 70% of the antioxidant factors present in the rosemary. This fraction of the natural antioxidants of the rosemary is then subjected to further fractionation by serial extraction with aqueous acid (to give a basic fraction), with bicarbonate at a pH of about 8.6% (to give a highly acidic fraction), and finally with alkali at a pH of about 11.5. This alkali-soluble fraction (called a weakly-acidic fraction) is separated from the so-called neutral fraction (acidic and basic insoluble fraction). The basic, highly acidic, and neutral fractions, all containing selected portions of the antioxidants present in rosemary, are discarded. The weakly-acidic fraction, containing the antioxidant compound of interest to Nakatani, is recovered from the alkali system by prompt acidification and extraction with ether and is considered his inventive antioxidant. He obtains 1.9 g of this material from 500 g of rosemary and from it isolates rosmanol. His yield is less than 3-4% of the total antioxidants present in the herb.
Nakatani, in describing the weakly-acidic fraction as requiring strong alkali (pH about 10.5, and preferably about 11.5, and using 4 extractions with 150 ml of 1N NaOH to solvate 1.9 g of the fractions in his example) explains why Viani could not extract all the antioxidant in his examples at his lower pH of about 8.6. The low solubility in aqueous alkali (less than 1.9 g/150 ml) is also apparent.
Although Nakatani does not refer to the instability of his 1.3% aqueous alkaline solution, it is necessary to recover the antioxidant from it immediately since it loses its activity in a matter of days. The explanation offered for the instability of Viani's solution applies here also.
In summary, the prior art shows that selected portions of the antioxidants present in rosemary are soluble at a level of not more than about 1% to 2% in aqueous media, at a pH of above about 8.5, more preferably above about 11.5. These preparations of antioxidants have been found to lose their antioxidant activity rapidly while in an alkaline solution. The same conclusions can be drawn for other Labiatae antioxidant preparations.
The art is replete with procedures for preparing and refining rosemary extracts. Kimura (U.S. Pat. No. 4,363,823) makes an alcohol extract, which, when added to boiling water, is separated from hydroscopic water-soluble substances and becomes a dry, insoluble powder upon cooling. This makes it similar in its constituents to a crude extract made with a less polar solvent, such as acetone or hexane. Berner (U.S. Pat. No. 3,732,111) extracts sage with an edible fat, removes volatiles with steam, and uses the extract in fat as an antioxidant. Chang (U.S. Pat. No. 3,950,266) describes a procedure for deodorization of rosemary extract in the presence of a nonvolatile edible oil. Bracco (U.S. Pat. No. 4,352,746) describes a process for carbonizing an extract which enables it to be deodorized and concentrated by molecular distillation. Kimura (U.S. Pat. No. 4,380,506) describes a technique for separating oil-soluble and oil-insoluble antioxidant fractions from an extract by using alcohol-water mixtures in the presence of hexane, and the efficacy of the oil-insoluble fraction as a bactericide. Hasegawa (Jap. patents 83-847974 and 84-247484) describes a process for deodorization of a solvent extract of an herb in the presence of an absorbent, and the concentration of the extract and washing with 20% to 50% solutions of methanol or ethanol for deodorization purposes. Of the prior art, only Nakatani and Viani suggest the use of alkaline pH's in their separation and deodorization procedures, and both of these investigators required the prompt neutralization of the aqueous alkaline extracts to recover the active principles in a stable acidic form.